Bone cell differentiation and bone synthesis induced by estrogen administration to male Japanese quail will be used to study several facets of these processes. Among these studies will be the analysis of bone samples taken when 3H-glucosamine and 35SO4 uptake increase sharply. This may allow us to discern the spectrum of glycosaminoglycans and other labeled compounds in order of their appearance during bone matrix formation. In another study the femurs of birds will be removed after specific periods of estrogen treatment and incubated with different isotopically labeled compounds to determine whether or not differentiation and bone synthesis will continue under in vitro condition. In further studies, samples of embryonic chick femur taken during early phases of mineralization will be used to study the intra and extracellular distribution of several elements important in the mineralization process. Comparison of this system with other calcification systems such as the avian shell gland will be made. Electron microprobe analysis of frozen thin sections and inert dehydration and embedding procedures will be used in these investigations.